Electronic devices, such as smartphones and other portable media devices, often include a speaker for reproducing sounds, such as speech from a telephone call or music from an audio/video file. Some such electronic devices are sized for portability, and thus include a microspeaker for the reproduction of sounds. The use of microspeakers presents challenges in that microspeakers can be highly variable in quality. One concern regarding microspeakers is over-excursion. Speakers reproduce sounds by driving a cone forwards and backwards to produce soundwaves. Over-excursion occurs when a signal driving the cone of the microspeaker causes the cone to extend beyond a safe operating region. Over-excursion may result in the cone making contact with a speaker casing and damaging the cone, permanently reducing the quality of output from the speaker. Furthermore, small electronic devices attempt to make up for the microspeaker's size by overdriving the microspeaker to maximize loudness. Conventionally, protection algorithms analyze the overdriving and attempt to prevent overdriving that can damage the microspeaker.
Conventional techniques for handling or preventing over-excursion include the use of speaker model within a speaker monitoring circuit. The speaker model may include a displacement model that estimates the cone displacement based on factors relating to operation of a speaker. The estimates may be used to determine and prevent speaker over-excursion. Existing displacement models operate by determining an electrical model of the speaker and converting the electrical model to a mechanical model. As shown in FIG. 1A, an adaptive filter Ha(s) may be developed using a monitored voltage and current for the speaker. The adaptive filter Ha(s) is an electrical model of the speaker. The Ha(s) model may be converted to obtain a mechanical model Hx(s). That mechanical model Hx(s) may be used to predict cone displacement based on an input audio signal S(t). An alternate conventional approach is shown in FIG. 1B. An adaptive filter Ha(s) may be developed using a monitored voltage and current for the speaker. Parameters are extracted from the adaptive filter Ha(s) and converted to form filter coefficients of a mechanical model Hx(s). That Hx(s) model is used to predict cone displacement based on an input audio signal S(t).
Each of these conventional techniques involves forming an electrical model of the speaker represented by an adaptive filter and converting that electrical model to a mechanical model capable of estimating cone displacement. However, the conversion process can be cumbersome. Furthermore, the conversion from electrical to mechanical parameters may require input regarding the mechanical parameters of the speaker. Thus, the conversion is not well-suited for operating on a wide range of types of speakers. For example, microspeakers are available in sealed-box and vented-box varieties that each have different mechanical parameters.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for audio circuitry for speaker monitoring and speaker protection employed in consumer-level devices, such as mobile phones. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above.